Daikin DPS - Dehumidification

Dehumidication
(See page 56 for more information)
In the dehumidication mode, mechanical cooling is used to
cool air low enough to wring moisture out of it. Hot Gas Reheat
or the standard unit heating equipment (Gas, SCR Electric
or Steam/Hot water) is used to raise the temperature of this
cooled air to a desirable value.
Dehumidication Initiation
Dehumidication operation can either be initiated based on a
eld installed (or network provided) humidity sensor input or set
for constant operation without regard to a humidity input.
Sensor Based Operation
When the Dehum Method= parameter is set to either Rel Hum
or DewPt, dehumidication initiation is based on a relative
humidity input or dewpoint calculated from a relative humidity
input. To calculate dewpoint from the humidity sensor input the
controller uses the temperature input selected with the Sensor
Loc = parameter. This can be set to Return, Space or OAT and
should be set to match the physical location of the humidity
sensor.
In this case dehumidication operation is initiated when
the relative humidity (or dewpoint) input rises above the
corresponding relative humidity (or dewpoint) set point by more
than ½ the deadband.
Continuous Operation
When the Dehum Method= parameter is set to Always,
dehumidication constantly active regardless of any relative
humidity sensor input.
Dehumidication Termination
Dehumidication operation is always terminated if cooling
operation is disabled for any reason, the Dehum Method=
parameter is set to None or if the Unit Status= indicates Off
Net, Off Sw, Off Alm or Off Man Ctrl.
In the case where the Dehum Method= parameter is set to
Rel Hum or DewPt, dehumidication operation is terminated
if the relative humidity (or dewpoint) input drops below the
corresponding relative humidity (or dewpoint) set point by more
than ½ the deadband.
In the case where the Dehum Method= parameter is set to
Always, dehumidication operation is never terminated unless
cooling operation is disabled or the Unit Status= indicates Off
Net, Off Sw, Off Alm or Off Man Ctrl.
Dehumidication Cooling Control
During dehumidication, control of cooling is based on the
Minimum Leaving Coil Temperature set point Mn Lvg Coil T
(Default = 45°F).
Cooling is controlled by a PI Loop to maintain the temperature
leaving the coil at the Mn Lvg Coil T. The normal DAT Cooling
Deadband and PI Loop parameters are used in this PI Loop.
Dehumidication Reheat Control
During dehumidication control, an analog Hot Gas Reheat
(HGRH) output or the standard modulating heating output is
controlled with a PI Loop to maintain the current Reheat Set
Point. If the Reheat Type software conguration parameter
is set to Modulating Hot Gas, an analog HGRH output is
controlled to maintain the Reheat Set Point. If the Reheat Type
software conguration parameter is set to Standard Heat, then
the normal heating analog output is controlled to maintain the
Reheat Set Point.
The effective Reheat Set Point varies depending on the current
unit operating state (Unit State=) as describe below.
Cooling Unit State
When dehumidication is active while the unit is in the Cooling
operating state, the effective Reheat Set Point is set equal
the current Discharge Air Cooling Set Point. For DAT units
the current Discharge Air Cooling Set Point is either xed or
varies based on a cooling discharge air reset schedule. For
zone control units the current Discharge Air Cooling Set Points
varies up and down based on the Control Temperature input
compared to the Occupied Cooling Set Point.
Fan Only Unit State
When dehumidication is active while the unit is in the Fan
Only operating state, the effect Reheat Set Point is normally
set based on the Control Temperature compared to the
Occupied Cooling Set Point and the Occupied Heating Set
Point.
The Reheat Set Point is set equal to the editable Maximum
Reheat Setpoint (Default 65°F) when the Control Temperature
drops to the Occupied Heating Setpoint and is set equal to the
editable Minimum Reheat Setpoint (Default 55°F) when the
Control Temperature rises to the Occupied Cooling Setpoint.
The Reheat Setpoint varies linearly between the minimum and
maximum when the Control Temperature is between the two
occupied setpoint values. This means that the temperature
leaving the unit is at a maximum just before the unit needs to
transition to the Heating operating state and at a minimum just
before needing to transition to the Cooling operating state.
OM 1141-3 • MICROTECH UNIT CONTROLLER 100 www.DaikinApplied.com
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